STANDARD INPUT

None.

INPUT FILES

None.

ENVIRONMENT VARIABLES

The following environment variables shall affect the execution of echo:

LANG

This variable shall determine the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_ ) do not specify a locale. See 2.6.

LC_ALL

This variable shall determine the locale to be used to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

LC_MESSAGES

This variable shall determine the language in which diagnostic messages should be written.

ASYNCHRONOUS EVENTS

Default.

STANDARD OUTPUT

The echo utility arguments shall be separated by single <space>s and a <newline> character shall follow the last argument.

STANDARD ERROR

Used only for diagnostic messages.

OUTPUT FILES

None.

EXAMPLES

As specified by this standard, echo writes its arguments in the simplest of ways. The two different historical versions of echo vary in fatal incompatible ways. The BSD echo checks the first argument for the string "−n", which causes it to suppress the <newline> character that would otherwise follow the final argument in the output. The System V echo does not support any options, but allows escape sequences within its operands: \a Write an <alert> character. \b Write a <backspace> character. \c Suppress the <newline> character that otherwise follows the final argument in the output. All characters following the \c in the arguments are ignored. \f Write a <form-feed> character. \n Write a <newline> character. \r Write a <carriage-return> character. \t Write a <tab> character. \v Write a <vertical-tab> character. \\ Write a backslash character. \0num Write an 8-bit value that is the 1-, 2-, or 3-digit octal number num. It is not possible to use echo portably across these two implementations unless both −n (as the first argument) and escape sequences are omitted. The printf utility (see printf(1) ) can be used to portably emulate any of the traditional behaviors of the echo utility as follows:

• The System V echo is equivalent to: printf "%b\n" "$∗"
• The BSD echo is equivalent to: if [ "X$1" = "X-n" ] then shift printf "%s" "$∗" else printf "%s\n" "$∗" fi

The echo utility does not support utility syntax guideline 10 because existing applications depend on echo to echo all of its arguments, except for the −n option

in the BSD version. New applications are encouraged to use printf instead of echo. The echo utility has not been made obsolescent because of its extremely widespread use in existing applications.

HISTORY OF DECISIONS MADE

In Draft 8, an attempt was made to merge the extensions of BSD and System V, supporting both −n and escape sequences. During initial ballot resolution, a −e option was proposed to enable the escape conventions. Both attempts failed, as there are historical scripts that would be broken by any attempt at reconciliation. Therefore, in Draft 9 only the simplest version of echo is presented. Implementation-defined extensions on BSD and System V will keep historical applications content. Portable applications that wish to do prompting without <newline>s or that could possibly be expecting to echo a "−n", should use the new printf utility (see printf(1) ), derived from the Ninth Edition. The LC_CTYPE variable is not cited because echo, as specified here, does not need to understand the characters in its arguments. The System V and BSD implementations might need to be sensitive to it because of their extensions.